Speaker
Description
Full metal walls are a high priority choice for future fusion reactors like ITER and CFETR, but they present significant challenges in plasma-wall interaction and high-Z impurity control. Low-Z material coatings (e.g., lithium, boron) are commonly employed to improve plasma confinement and achieve H-mode, but they add considerable complexity to reactor operation and maintenance due to tritium retention in co-deposits.
To investigate the feasibility of achieving H-mode plasmas without relying on any low-Z material coating on full metal walls, a trial experiment was carried out in EAST superconducting tokamak with molybdenum first walls and tungsten divertors. Long-term baking and GDC/ICRF associated plasma cleanings were used for light impurities removal, and ECRH was used for pre-ionization and central heating to prevent tungsten impurity penetration into the plasma core.
Following one week air exposure for maintenance in the 2025 spring campaign, solely through a few days baking and GDC/ICRF seven consecutive stable H-mode plasmas (Ip ~400kA, ne~4.5×1019/m³, duration >14s, 1.95 MW ECRH+ 1 MW LHCD+0.2 MW ICRH auxiliary heating) were successfully realized after 461 plasma discharges exercises. In these H-mode plasmas, the H₉₈(y,2) factor ranged from 0.95 to 1.0, the plasma stored energy was approximately 130 kJ.
This result validates that even without a low-Z coating, EAST can still achieve high-performance plasma operation, but it requires intensive impurities removal and an effective heating scheme. This research provides a good reference for H-mode plasma operation in future fusion reactors with full metal walls with potentially simplifying wall conditioning strategies and reducing operational complexity. This research was funded by National Key Research and Development Program of China (2024YEF03000200).